U.S. Pat. No. 4,879,007 discloses a floating shield for use in an electrolytic bath. The shield includes an elongated trough in which substrates are loaded for plating. The substrates are held in the trough in a vertical plane, and with the lower edges of the substrates below the plane of the upper edges of the trough. Immersed into the bath are a pair of anodes, each extending parallel to the longitudinal axis of the floating shield. The substrates loaded in the trough are connected to a cathode bus bar by one or more clamps. In operation, electric current passes between the anodes and the cathode bus bar through electrolyte contained in the bath, and thereby to electroplate the substrates.
When a plating factory orders an electroplating apparatus from a manufacturer, it is necessary to specify the "board size" of the substrates intended to be plated by the apparatus. In this connection, "board size" means the vertical length of the substrate when such is held in a vertical plane. It is also a usual practice in the relevant field to so arrange the depth of the floating shield in the bath that the top edge of the substrates is of a fixed distance from the top edge of the bath. The manufacturer will then arrange the dimensions of the bath, the anodes and the depth of the trough in the bath such that there will be a satisfactory and uniform electroplating result. It is found in practice that if substrates of a board size shorter than the intended board size are electroplated in the bath, the lower edges of the substrates will be "over-plated". This is known as "edging effect" and means that the metal deposited on or around the lower edges of the substrates is thicker than that deposited in the rest of the substrates.
While it is possible to reduce this "edging effect" by changing the anodes used in each electroplating task, as there may be over forty anodes in a single tank, and they are very heavy, it is very difficult and not practical to replace anodes.
It is therefore an object of the present invention to provide an improved electroplating apparatus in which the aforesaid shortcoming is mitigated, or at least to provide a useful alternative to the trade.